Combination igniter and temperature sensor



Feb. 17, 1970 v J. R. WILLSON 3,495,925

COMBINATION IGNI'IER AND TEMPERATURE SENSOR Filed June 11, 1968 W lN-VENTQRS 1 JAMES R; WILLSON I ATTQRNEYS United States Patent 3,495,925 COMBINATION IGNITER AND TEMPERATURE SENSOR James R. Willson, Garden Grove, Califl, assignor to Robertshaw Controls Company, Richmond, Va., a corporation of Delaware Filed June 11, 1968, Ser. No. 736,205 Int. Cl. F23n /02; F23q 2/28 US. Cl. 43166 Claims ABSTRACT OF THE DISCLOSURE A combination igniter and temperature sensor comprising a coaxial assembly having an inner conductor extending through the center of the coaxial assembly, a ring of thermistor material concentrically surrounding the inner conductor, an outer conductor concentrically surrounding the ring of thermistor material, a sheath of insulating material concentrically surrounding the outer conductor, and an igniting coil wound around the sheath and connected to the inner conductor at the top of the assembly.

BACKGROUND OF THE INVENTION The present invention pertains to an igniter for fuel burner apparatus and more particularly to a combination igniter and temperature sensor for use in controlling burner apparatus. 1

Conventional automatic ignition and safety shut-off apparatus for burners include standing pilotsand electric igniters. Systems using a standing pilot and a thermocouple for sensing the pilot flame have the disadvantage of being subject to drafts, high ambient temperatures and clogging from lint and dust. Electric igniters have been used for indirect ignition by igniting a pilot and direct ingition. Indirect ignition using electric igniters has the same disadvantages as the standing pilot systems and, consequently, direct ignition is the most desirable. In the past, complex circuitry has been necessary in order to prove the flame or ignition temperature of the electric igniter in direct ignition systems,-and the electric igniter and the flame sensing means or ignition temperature proving means have been separate units causing difliculty in installation and repair.

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to construct a single device operable as both an igniter and a temperature sensor.

A further object of the present invention is to combine an igniter and a temperature sensor in a single coaxial assembly.

Another object of the present invention is to construct a combination igniter and temperature sensor having only three terminals.

The present invention has another object in that a com bination igniter and temperature sensor is constructed having only two terminals.

Another object of the present invention is to assemble a dual function device having a thermistor disposed within an igniting coil.

Yet another object of the present invention is to utilize a single device as an igniter and an igniter proving means.

A further object of the present invention is to construct 3,495,925 Patented Feb. 17, 1970 "ice an igniter in a coaxial assembly with a temperature sensor for proving the temperature of the igniter.

The present invention has another object in that a combination igniter and flame sensor is constructed .in a coaxial assembly.

The present invention is characterized in thata combined igniting and temperature sensing device includes an insulating casing, an igniting coil would around the casing, a conductor disposed within the casing and a thermistor disposed within the casing and connected with the conductor.

Other objects and advantages of the present invention will become apparent from the following description of the preferred embodiments as shown in the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic diagram of a burner control system utilizing a combined igniter and temperature sensor in accordance with the present invention;

FIG. 2 is a perspective view of a three terminal combination igniter and temperature sensor in accordance with the present invention;

FIG. 3 is a side elevation with parts in section of the coaxial assembly of the three terminal combination igniter and temperature sensor shown in FIG. 2;

FIG. 4 is a side elevation with parts in section of a two terminal combination igniter and temperature sensor in accordance with the present invention; and

FIG. 5 is a schematic diagram of a burner control system utilizing the combination igniter and temperature sensor of FIGS. 2 and 3.

DESCRIPTION OF THE PREFERRED EMBODIMENT A burner control system using a three terminal combination igniter and temperature sensor according to the present invention is shown in FIG. 1 and includes a burner 10 having a flow of fuel thereto under the control of a valve 12. A pair of power leads 14 and 16 are adapted to be connected to any suitable conventional source of electrical energy. Lead '14 is connected through a switch 18 and a heating coil 20 to lead 16 and through switch 18 and a solenoid 22 for valve 12 to a junction 24 which connects with lead 16 through the parallel combination of a bimetal element 26 and a contact 28 in series and a terminal 30, a thermistor 32 and a terminal 34. Lead 14 also connects with lead 16 through switch 18, a terminal 36, an electric igniter 38 and terminal 34. Thermistor 32 and igniter 38 are formed in a single device 40 which is located within igniting and flame sensing proximity of burner 10.

In order to simplify the description of the operation of of FIG. 1, it is being described in conjunction with a heating system; however, the present invention has many uses in many systems and is not intended to be limited to heating systems. Switch 18 may be an automatic thermostat, or it may be manually operated. In either case, When heat is desired switch 18 is closed to energize igniter 38 and cause current to flow through heating coil 20. Due to the negative temperature coefiicient of thermistor 32, it exhibits an extremely high resistance and is eifectively nonconducting before burner 10 is ignited; however, solenoir 22 is energized to open valve 12 due to the current path through bimetal 26 and contact 28.

After igniter 38 heats to igniting temperature, burner is ignited," and'the'rmistor 32 senses the flame at burner 10 which lowers its resistance to allow it to conduct and provide a current path to maintain valve 12 open after bimetal 26 warps to open contact 28 due to the heat from coil 20. With proper ignition, the system will now be in its full heating condition in which igniter 38 is energized, thermistor 32 is conducting, valve 12 is open, and contact 28 is open. The system will continue in its full heating condition until switch 18 is opened; however, should-the flame at burner 10 be extinguished for some reason, thermistor 32 will become nonconducting to 'deenergize solenoid 22 and close valve 12 and place the system in a lock-out condition. T o reset the system from its lock-out condition, switch 18 is opened and then closed again after heating coil 20 has cooled sufiiciently to allow bimetal 26 and contact 28 to close.

I If, after switch 18 is closed, ignition does not occur by the time bimetal 26 is heated sufliciently to warp and move away from contact 28, thermistor 32 will remain nonconducting to deenergize solenoid 22 and close valve 12 to stop the flow of fuel to burner 10. The system will now be in its lock-out condition which requires opening of switch 18 for resetting as previously explained.

When the need for heat has been satisfied, the system may be shut down by opening switch 18 which closes valve 12, deenergizes igniter 38 and deenergizes heating coil 20 which allows bimetal 26 to cool and move back so that it meets contact 28 to prepare the system for its next cycle.

The combination igniter and temperature sensor of FIG. 1 is illustrated in perspective in FIG. 2 and in section in FIG. 3, and identical reference numerals are used to identify identical elements in FIGS. 1, 2 and 3. As shown in FIGS. 2 and 3, device 40 is a coaxial assembly having an outer hollow cylindrically shaped ceramic insulating sheath 42, an outer hollow cylindrically shaped conductor 44 disposed adjacent the inside of insulating sheath 42, a cylindrically shaped ring of thermistor material 32 having a large negative temperature coefiicient disposed adjacent the inside of conductor 44, and an inner conductor 46 extending through the center of the coaxial assembly. A first terminal 36 connects with a coil 38 wound around insulating sheath 42 to act as an igniter. At the top of device 40, coil 38 connects with inner conductor 46 through a radially extending conductor 48, and inner conductor 46 is connected to a second terminal 34 at the bottom of device 40. Outer conductor 30 is connected to a third terminal 30 at the bottom of device 40. The coaxial igniter and temperature sensor assembly is mounted on a support block 50 to permit easy attachment in a system. Thermistor 32 may be constructed of any conventional material, such as a semiconductor material having the requisite large negative temperature coeflicient and may be deposited on conductor 46, or it may be an independent assembly.

Combination igniter and temperature sensor 40 may be positioned adjacent a port of a burner in such a manner that coil 38 serves to ignite the burner, and thermistor 32 senses a flame at the burner, or combination igniter and temperature sensor 40 may be used to prove ignition temperature as will be explained with respect to FIG. 5. The coaxial assembly of device 40 enables thermistor 32 to be exposed to low operating temperatures since thermistor 32 is insulated from igniter coil 38 by ceramic insulating sheath 42.

Terminal 30 is connected to terminal 34 through outer conductor 44, thermistor 32 and inner conductor 46; and, consequently, conduction from terminal 30 to terminal 34 is dependent upon the resistance exhibited by thermistor 32. As previously noted, thermistor 32 has a large negative temperature coefficient, and it may be designed to substantially conduct current at any desired temperature such as ignition temperature or flame temperature. When thermistor 32 does not sense the desired temperature for substantial conduction, it presents a high resistance. 'Igniter coil 38 is connected at one end to terminal 36 and at its other end to terminal 34 through inner conductor 46.

A modification of the embodiment of FIGS. 2 and 3 is illustrated in FIG. 4, and identical reference numerals are employed in FIG. 4 to designate parts identical to FIGS. 2 and 3. i

FIG. 4 illustrates an embodiment of the combination igniter and temperature sensor of the present invention used as a parallel resistance-operated device 50. Device 50 is identical in structure to device 40 except that only two terminals 34 and 52 are provided with terminal 52 connected to both igniter 38 and conductor 44. The connection of both igniter 38 and conductor 44 to terminal 52 places igniter 38 and thermistor 32 in parallel between terminals 52 and 34, and their parallel network resistance may be used as a control means.

For example, when used in a flame proving burner control system, igniter 38 may be a tungsten glow-wire having a resistance of ohms at ignition temperature and 25 ohms at room temperature, and thermistor 32 may have an extremely high resistance when not exposed to a flame and a resistance of 10 ohms when exposed to a flame. Thus, when power is initially applied to device 50, its resistance will be approximately 25 ohms since the resist: ance of thermistor 32 is many times greater than the 25 ohm resistance of igniter 38 at room temperature. When igniter 38 has been heated to igniting temperature, the resistance of device 50 will be approximately 10' ohms if a flame is sensed since the resistance of thermistor 32 is 10 ohms in the presence of a flame and the resistance of igniter 38 is 150 ohms at igniting temperature. If a flame is not sensed, the resistance of thermistor 32 is much greater than the 150 ohm resistance of igniter 38; and, consequently, the resistance of device 50 is approximately 150 ohms. Thus, a control system may be operated in response to the resistance of device 50.

The above example is intended to illustrate the use of a two terminal combination igniter and temperature sensor in a three state, resistance-operated control system. That is, a first resistance state is defined upon initial application of power, a second resistance state is defined when igniter 38 is heated to igniting temperature and a flame is sensed, and a third resistance state is defined when igniter 38 is heated to igniting temperature but a flame is not sensed. However, it is clear that this is but one example of the manner in which the two terminal combination igniter and temperature sensor of the present invention may be utilized.

The combination igniter and heat sensor illustrated in FIGS. 2 and 3 may be utilized to provide an igniter proving function by merely constructing thermistor 32 of a material with a smaller negative temperature coeflicient than that utilized for flame sensing. Thus, thermistor 32 will have a low resistance when igniter 38 obtains igniting temperature and will have a high resistance when igniter 38 is below igniting temperature. .This igniter proving function is possible because the flame temperature for most gases used for combustion is 3 to 4'times greater than their respective ignition temperatures at atmospheric pressure. Thus, the device of FIGS. 2 and 3 can be utilized in. one application for flame sensing with the igniter at igniting temperature and in another application for sensing igniting temperatures; it being of no consequence if the temperature sensed by the thermistor is greater than igniting temperature. i Y i A burner control system utilizing a device according to the present invention as a combination igniter and igniter prover is illustrated in FIG. 5. Such use of the combination device of the present invention is etfectively an electric pilot in that ignition capability is continually monitored by the thermistor. The system of FIG. 5 will be described utilizing reference numerals identical to those used in FIG. 1 for identical parts and reference numerals with 100 added for similar parts.

The burner control system of FIG. 5 includes a burner having a flow of fuel thereto under the control of a valve 12. A pair of power leads 14 and 16 are adapted to be connected to any suitable conventional source of electrical energy. Lead 14 is connected through a switch 18, a solenoid 22 for valve 12, a terminal 30, a thermistor 132, and a terminal 34 to lead 16 and through switch 18, a terminal 36, an electric igniter 38 and terminal 34 to lead 16. e

Again, "as with the description of FIG. 1, the operation of the system of FIG. 5 is described in conjunction with a heating system; however, the present invention has many uses ,in many systems and is not intended to be limited to heating systems. Switch 18 may be manually operated or may be an automatic thermostat; however, in either case switch 18 is closed when there isa demand for heat. The closure of switch 18 completes a circuit from lead 14 through switch 18 and igniter 38 to lead 16 thereby energizing igniter 38. The circuit from lead 14 through Iswitch 18, solenoid 22-and thermistor 132 is not completed due to the high resistance of thermistor 132 at low-temperatures. However, as igniter 38 begins to heat, the resistance of thermistor 132 drops, and when igniter 38 obtains igniting temperature the resistance of thermistor 132 will have dropped low enough to permit sufficient current to flow therethrough to energize solenoid 22 and open valve 12. Thus, it is seen that valve 12 will not open to permit fuel flow to burner 10* until igniter 38 is heated to igniting temperature thereby providing safe operation of the system without the loss of fuel during the interim between heat demand and obtention of igniting temperature by igniter 38.

If igniter, 38 should drop below igniting temperature, for any reason, during full heating operation the resistance of thermistor 132 will increase to cause deenergization of solenoid 22 and closure of valve 12 to shut down the system. However, the system will automatically recycle once igniter 38 again obtains igniting temperature to decrease the resistance of thermistor 132 and open valve 12.

After the need for heat is satisfied, switch 18 is opened to open all circuits and shut down the system.

Thus, it is seen that the use of the combination igniter and temperature sensor has many uses which require only simple circuitry and yet provide the required safety for burner systems.

The compact coaxial assembly of the combined igniting and temperature sensing devices of the present invention coupled with the use of only two or three terminals or leads to provide both an igniting function and an igniter proving function or a flame sensing function permits the combination device of the present invention to be utilized in systems with simplified circuitry and to be utilized more efficiently with conventional burners.

Inasmuch as the present invention is subject to many modifications, variations and changes in detail, it is intended that all matter contained in'the foregoing description or shown in the drawing shall be interpreted as illustrative and not in a limiting sense.

What is claimed is:

1. A combination igniter and temperature sensor comprising insulating means,

electrical igniting means disposed on said insulating means,

temperature responsive resistance means disposed within said insulating means, and

electrical connecting means including a conductor disposed within said insulating means and connected with said temperature responsive resistance means.

2. The invention as recited in claim 1 wherein said electrical connecting means further includes a second conductor formed concentrically with said first mentioned conductor, and said temperature responsive resistance means has a negative temperature coefiicient and is formed concentrically with said first and second conductors and disposed therebetween.

3. The invention as recited in claim 2 wherein said insulating means includes a sheath formed concentrically with said first and second conductors and disposed adjacent said second conductor, and said electrical igniting means includes an igniter coil wound around the sheath of said insulating means.

4. The invention as recited in claim 3 wherein said electrical connecting means includes means connecting a first end of said igniting means with said first conductor and said temperature responsive resistance mean is electrically connected with said first conductor and said second conductor.

5. The invention as recited in claim 4 wherein said electrical connecting means includes first, second and third terminals, means connecting said first coductor with said first terminal, means connecting said second conductor with said second terminal and means connecting a second end of said igniting means with said third terminal.

6. The invention as recited in claim 4 wherein said electrical connecting means includes first and second terminals, means connecting said first conductor with said first terminal, and means connecting a second end of said igniting means and said second conductor to said second terminal.

7. A dual function device comprising insulating means,

electrical igniting means wound around said insulating means,

electrical conductor means disposed within said insulating means; and

temperature responsive resistance means disposed within said insulating means and connected with said electrical conductor means.

8. The invention as recited in claim 7 wherein said insulating means is formed in a hollow cylindrical shape, said electrical conductor means includes a first conductor and second conductor formed concentrically with each other, and said temperature responsive resistance means has a negative temperature coefiicient and is formed in a hollow cylindrical shape and is disposed between said first and second conductors.

9. In a combined igniting and flame sensing device, a coaxial assembly comprising a first conductor,

flame sensing means including a ring of thermistor material having a negative temperature coefificient and formed in a hollow cylindrical shape surrounding and concentric with said first conductor,

a second conductor formed in a hollow cylindrical shape surrounding and concentric with said ring of thermistor material,

an insulator formed in a hollow cylindrical shape surrounding and concentric with said second conductor, and

an igniting coil wound around said insulating and connected with said first conductor.

10. In a combined igniter and igniter proving device, a

coaxial assembly comprising a first conductor,

igniter proving means including a ring of thermistor material having a negative temperature coefiicient and formed in a hollow cylindrical shape surrounding and concentric with said first conductor,

a second conductor formed in a. hollow cylindrical shape surrounding and concentric with said ring of thermistor material,

a second conductor formed in a hollow cylindrical shape surrounding and concentric with said ring of thermistor material,

an insulator formed in a hollow cylindrical shape sur- 7 '8 rounding and concentric with said second conductor, FQREIGN PATENTS and 650,237 10/1962 Canada.

an igniting coil wound around said insulator and con:

nected with said first conductor. KENNETH W. ,SPRAGUECPrimary am References Cited 3 v i i 3 UNITED STATES PATENTS 431 69 30 3,393,038 7/1968 Burkhalter et a1. 43166 US. Cl. X.R. 

